The invention has particular application to a method of and system for delivering a treatment substance to dense non-aqueous phase liquids (DNAPLs) and their associated dissolved phase contaminant plumes in a treatment zone for the purpose of removing and/or remediating contaminants from the zone. However, it will be understood that the invention has other applications such as delivery of a treatment substance to light non-aqueous phase liquids (LNAPLs) and heap leaching processes.
Dense non-aqueous phase liquids (DNAPLs) have been widely used in industry since the beginning of the 20th century. DNAPLs are only slightly soluble in water and being denser than water tend to migrate to regions below the water table where they slowly dissolve into flowing groundwater. As a consequence, a release of DNAPLs can lead to long term contamination of groundwater. Common DNAPLs include creosote, transformer and insulating oils containing polychlorinated biphenyls (PCB), coal tar, and chlorinated solvents such as trichloroethylene (TCE) and tetrachloroethylene (PCE).
Treatment of sub-surface zones contaminated with DNAPLs is difficult because of uncertainty as to location of the DNAPLs in the sub-surface environment, and because the sub-surface architecture is generally heterogeneous and complex.
An example of an existing method of treating a contaminated sub-surface zone is shown in FIGS. 1 and 2.
In FIG. 1, a sub-surface zone 10 is exposed to a contaminant 12 emanating from a contaminant source 14. Since the contaminant is a DNAPL, the contaminant 12 is relatively dense and migrates downwardly past the water table 16, through relatively high permeability portions 18 of the sub-surface zone 10 and around relatively low permeability portions 20.
As shown in FIG. 2, after a prolonged period of time the contaminant 12 diffuses and advects outwardly into the surrounding high and low permeability portions 18, 20.
In order to remediate the contaminated sub-surface zone 10, a boring device 22 is used to bore a hole 24 in the sub-surface zone 10, and a treatment substance is pumped into the hole 24. The treatment substance subsequently migrates into the surrounding sub-surface and destroys or neutralizes any contaminant encountered. However, with this method it is difficult to ensure that the treatment substance is delivered to all contaminant material in the sub-surface zone, and in particular it is difficult to ensure migration of the treatment substance into relatively low permeability portions of the sub-surface zone as this migration is limited to the relatively slow rates of molecular diffusion. As a consequence, methods for treating NAPL contaminants and their associated dissolved portions in sub-surface zones have hitherto had limited success.